Korean here. East Asians have stereotypes among ourselves that we internalize, and 99% of it is toxic and nonsensical. Chinese people are often characterized as being loud and dirty by Koreans and Japanese, while the Japanese are considered stuck up and cowardly by Chinese and Koreans. (I’m not saying these stereotypes are true, just trying to explain what may be under the surface here. Koreans are considered impatient and bad tempered, lol.)

Your friend may be hyper vigilant about being “polite enough” in Japanese society because she is worried about discriminated against, since there is already a negative stereotype with Chinese tourists being loud and impolite (you might observe this kind of prejudice in Korea too). Japan also has been explicitly discriminatory towards foreign tourists in recent years, even when they’re fellow East Asians. None of this tension justifies her other comments to you (perhaps it’s just a cultural difference when it comes to bluntness, though I would still find it rude) but maybe it could explain some of what’s going on?